Additional liquid natural gas plant and method of operating thereof

ABSTRACT

The invention relates to a liquid natural gas plant for producing liquefied natural gas. The liquid natural gas plant comprises two or more parallel treatment and liquefaction trains, each train comprising a cooling stage arranged to receive a cleaned natural gas stream from a gas treatment stage, an NGL-extraction unit for extracting natural gas liquids, thereby generating a light natural gas stream. The liquid natural gas plant comprises an additional liquefaction train, comprising an additional cooling stage arranged to receive an additional feed stream for generating additional liquefied natural gas. The additional feed stream comprises two or more side streams taken from the light natural gas taken from the respective light natural gas streams of the one or more parallel treatment and liquefaction trains.

FIELD OF THE INVENTION

The present invention is directed to liquid natural gas plant comprisinga plurality of treatment and liquefaction trains. The invention isfurther related to a method of retrofitting and/or operating such aliquid natural gas plant.

BACKGROUND TO THE INVENTION

Natural gas can be liquefied for purposes of storage and transportation,as it is occupying a smaller volume in liquid state than in gaseousstate. Typically, before being liquefied, the natural gas is treated toremove contaminants (such as H₂O, CO₂, H₂S and the like) and heavyhydrocarbon molecules, which may freeze out during the liquefactionprocess.

Liquefaction of natural gas is an energy consuming process. Designingand operating liquid natural gas plants in the most efficient manner istherefore a constant focus area.

WO2006/120127 describes an LNG plant having a single liquefaction trainfor providing LNG in liquid or “pseudo-liquid” form. The LNG in liquidor “pseudo-liquid” form is sent into a separation unit for providingpurified LNG and a nitrogen-enriched stream.

WO201576975 describes a method of retrofitting a full-scale LNG plant toenhance the LNG production capacity of the LNG plant and a method foroperating such a retrofit plant. A small scale LNG plant having acapacity less than 2 MTPA can be integrated with a main LNG plant havinga capacity of at least 4 MTPA such that end flash gas and boil off gasfrom the main LNG plant can be liquefied by the small scale LNG plant asincremental LNG. According to WO201576975 the production capacity of theintegrated system can be improved by increasing the temperature of thegas stream exiting the main cryogenic heat exchanger of the main LNGplant between 5° C. and 30° C. as compared with the design temperature.

WO2006009646 is related to hydrocarbon fluid processing plants, methodsof designing hydrocarbon fluid processing plants, methods of operatinghydrocarbon fluid processing plants, and methods of producinghydrocarbon fluids using hydrocarbon fluid processing plants. Moreparticularly, some embodiments of the invention are related to naturalgas liquefaction plants, methods of designing natural gas liquefactionplants, methods of operating natural gas liquefaction plants and methodsof producing LNG using natural gas liquefaction plants. One embodimentof the invention includes a hydrocarbon fluid processing plant includinga plurality of process unit module types, the plurality of process unitmodule types including at least a first process unit module typeincluding one or more first process unit modules and a second processunit module type including two or more integrated second process unitmodules wherein at least one of the first process unit modules and atleast one of the second process unit modules are sized at theirrespective substantially maximum processing efficiency.

SUMMARY OF THE INVENTION

It is an aim to provide a more efficient LNG plant.

In one aspect the present invention is directed to a liquid natural gasplant for producing liquefied natural gas from a contaminated naturalgas feed stream, the liquid natural gas plant comprising two or moreparallel treatment and liquefaction trains arranged in process portionsof the contaminated natural gas feed stream in parallel, the treatmentand liquefaction trains each comprising:

-   -   an inlet for receiving a portion of the contaminated natural gas        feed stream,    -   a gas treatment stage for removing contaminants from the        respective portion of the contaminated natural gas feed stream)        thereby generating a cleaned natural gas stream,    -   a cooling stage arranged to receive the cleaned natural gas        stream from the gas treatment stage for cooling at least part of        the cleaned natural gas stream, wherein the cooling stage        comprises an NGL-extraction unit for extracting natural gas        liquids, thereby generating a light natural gas stream to be at        least partially further cooled by the cooling stage to be at        least partially liquefied and    -   an outlet for discharging liquefied natural gas,

wherein the liquid natural gas plant comprises at least one additionalliquefaction train, the additional liquefaction train comprising:

-   -   an inlet for receiving an additional feed stream,    -   an additional cooling stage arranged to receive the additional        feed stream for cooling the additional feed stream thereby        generating additional liquefied natural gas, and    -   an outlet for discharging the additional liquefied natural gas,

wherein the additional feed stream comprises two or more side streamstaken from the respective light natural gas streams of the two or moreparallel treatment and liquefaction trains.

The liquid natural gas plant as defined above also encompasses liquidnatural gas plants comprising more than one additional liquefactiontrain.

NGL-extraction unit for extracting natural gas liquids may be performedon any suitable natural gas stream in the cooling stage. According to anembodiment, the cooling stage comprises a first cooling unit, arrangedto generate a pre-cooled cleaned natural gas stream and a second coolingunit arranged to generate a further cooled stream. NGL-extraction unitfor extracting natural gas liquids may be performed on the pre-cooledcleaned natural gas stream.

The inlet of the additional liquefaction train is directly or indirectlyin fluid connection with conduits in the respective treatment andliquefaction trains which in use carry the respective light natural gasstreams. Furthermore, the inlet of the additional liquefaction train isdirectly or indirectly in fluid connection with conduits in therespective treatment and liquefaction trains carrying any furtherstreams to be comprised by the additional feed stream.

The additional feed stream may comprise further streams, including oneor more side streams of natural gas taken downstream from the inlet ofthe respective treatment and liquefaction trains, such as an end flashstream, a boil-off gas stream (taken from one or more LNG storagetanks), the cleaned natural gas stream. The gas treatment stage maycomprise one or more gas treatment units (as explained in more detailbelow). The additional feed stream may further optionally comprise oneor more side streams taken from intermediate partially cleaned naturalgas streams in between respective gas treatment units.

Additionally, or alternatively, the additional feed stream may comprisefurther streams obtained from a fractionation unit provided to receiveand fractionate the natural gas liquids obtained from the NGL-extractionunit. The further stream may in particular be at least a portion of oneor more methane enriched streams generated by respective fractionationunits and/or at least a portion of one or more ethane enriched streamsgenerated by respective fractionation units.

Depending on the composition of the additional feed stream, theadditional liquefaction train may comprise some gas treatment units andmay comprise a NGL-extraction unit.

However, according to an embodiment, at least 30 mol % of the additionalfeed stream is formed from the respective light natural gas streamsgenerated by the NGL-extraction units. According to a preferredembodiment at least 50 mol %, or at least 75 mol % of the additionalfeed stream, e.g. 100 mol %, is formed from the respective light naturalgas streams generated by the NGL-extraction units. The additional feedstream may only be formed form the respective light natural gas streams.The light natural gas stream generated by the NGL-extraction unit areclean, lean and at a relatively high pressure, so do not require anyfurther gas treatment units and need no or relatively littlecompression. The more of the additional feed stream is formed by therespective light natural gas streams, the less compression and gastreatment is needed with respect to the additional liquefaction train.

The additional liquefaction train preferably doesn't comprise aNGL-extraction unit, as the additional feed stream, at least partiallyand preferably for at least 30 mol %, at least 50 mol % or at least 75mol % already passed through a NGL-extraction unit. According to anembodiment, the additional liquefaction train comprises a relativelysmall NHL-extraction unit only. The additional liquefaction trainrequires a relatively small gas treatment stage with only a subset ofthe gas treatment units of the treatment and liquefaction train andpreferably doesn't comprise a gas treatment stage as the additional feedstream is already cleaned. Therefore, the additional liquefaction trainrequires less hardware and is relatively cheap, both in terms of capitalinvestment costs as well as in operational costs.

By combining streams from two or more parallel treatment andliquefaction trains, the additional liquefaction train can be given aconsiderable size to benefit from economy of scale.

The respective light natural gas streams of the one or more paralleltreatment and liquefaction trains may be referred to as C₁-enrichedstream or C₂ ⁺-depleted streams. The respective light natural gasstreams may for instance be obtained from the vapour phase of the refluxvessel of a scrub column, in which case the light natural gas streamsmay be at a temperature in the range of minus 40° C.-minus 50° C., e.g.minus 45° C., and at a pressure in the range of 40-55 bara. Side streamstaken from these light natural gas stream to be comprised in theadditional feed stream can be passed to the additional liquefactiontrain directly, i.e. without recompression.

The light natural gas streams may also be heat integrated with a firstor pre-cooling unit to recover at least some of the cold present inthese streams before obtaining a side stream. In such an embodiment, theside streams taken from the light natural gas streams after coldrecovery may be at a temperature in the range of +10° C.-+20° C., e.g.+15° C., and at a pressure in the range of 40-55 bara.

Preferably, the respective light natural gas streams are heat-integratedwith pre-cool step, especially when a collecting and compression unit isprovided (collecting and compression unit will be explained in moredetail below).

The side streams taken from the respective light natural gas streamshave a relatively high pressure related to the pressure of thecontaminated natural gas feed stream and/or the cleaned natural gasstream (30-100 bar) which can be fed into the additional liquefactiontrain, without recompression or with moderate recompression only. Incertain embodiments, the pressure of the additional feed stream isselected higher (e.g. 10 or 20 bar higher) than the pressure of thecontaminated natural gas feed stream to facilitate efficient cooling andliquefaction, which higher pressure can be obtained at relatively lowcosts given the relatively high pressure of at least some of the streamscomprised by the additional feed stream.

In another aspect there is provided a method of retrofitting an existingliquid natural gas plant to increase the liquefied natural gasproduction capacity thereof, wherein the existing liquid natural gasplant comprises two or more parallel treatment and liquefaction trainsfor producing liquefied natural gas from a contaminated natural gas feedstream, wherein the two or more parallel treatment and liquefactiontrains are arranged to process portions of the contaminated natural gasfeed stream in parallel and are each arranged to:

-   -   receive a portion of a contaminated natural gas feed stream,    -   remove contaminants from the respective portion of the        contaminated natural gas feed stream thereby generating a        cleaned natural gas stream,    -   cool at least part of the cleaned natural gas stream and extract        natural gas liquids, thereby generating a light natural gas        stream to be at least partially further cooled by the cooling        stage,

wherein the method of retrofitting comprises

-   -   providing an additional liquefaction train, the additional        liquefaction train comprising an additional cooling stage        arranged to receive and liquefy an additional feed stream to        generate additional liquefied natural gas,    -   fluidly connecting the additional liquefaction train to two or        more of the light natural gas streams of two or more of the        treatment and liquefaction trains to obtain side streams of the        two or more light natural gas streams to be comprised in the        additional feed stream, thereby creating a retrofitted liquid        natural gas plant.

The method may further comprise fluidly connecting the additionalliquefaction train to one or more further streams (as described above),including side streams taken downstream from the inlet of the treatmentand liquefaction trains, such as from an end flash stream, a boil-offgas stream (taken from one or more LNG storage tanks, the cleanednatural gas stream, an intermediate partially cleaned natural gasstreams in between respective gas treatment units and side streamsobtained from a fractionation unit provided to receive and fractionatethe natural gas liquids obtained from the NGL-extraction unit (e.g. sidestreams from one or more methane enriched streams and/or one or moreethane enriched streams).

The additional liquefaction train may be as described above. Theadditional liquefaction train may preferably not comprise aNGL-extraction unit, as the additional feed stream already passedthrough a NGL-extraction unit. The additional liquefaction train mayalso not comprise a gas treatment stage as the additional feed stream isalready cleaned.

The method may further comprise debottlenecking the existing liquidnatural gas plant, for instance by replacing or maintaining parts of theexisting LNG plant, in particular upstream of the position where naturalgas liquids are extracted. Debottlenecking means improving the designthroughput of the existing liquid natural gas plant by increasing thedesign throughput of the most constraining part of the liquid naturalgas plant.

The method of retrofitting is in particular advantageous in situationsin which the capacity of the warm ends, i.e. the pre-treatment unit(described in more detail below), the gas treatment stage, the NGLextraction unit were designed for a richer and more contaminated gascomposition than actually experienced, thereby resulting in spare ullagein the warm ends of the treatment and liquefaction trains, while thecold end, i.e. the equipment downstream of the NGL extraction unit, arealready working at or close to their design capacity.

Furthermore, this method is in particular advantageous when the existingtreatment and liquefaction trains are constrained by the available gasturbine power output, limiting the available refrigeration capacity.

According to a further aspect there is provided a method of operating a(retrofitted) liquid natural gas plant as described above, wherein themethod comprises

-   -   operating the two or more parallel treatment and liquefaction        trains whereby operating the two or more parallel treatment and        liquefaction trains comprises receiving respective portions of        the contaminated natural gas feed streams by the two or more        parallel treatment and liquefaction trains at a feed pressure        and    -   operating the additional liquefaction train, whereby operating        the additional liquefaction train comprises providing an        additional feed stream comprising two or more light natural gas        streams taken from the two or more parallel treatment and        liquefaction trains (A, B), wherein the additional feed stream        is provided at an additional feed pressure, being at least 10        bar above the feed pressure.

Similar to above, the additional feed stream may comprise one or morefurther streams, including side streams taken downstream from the inletof the treatment and liquefaction trains, such as from an end flashstream, a boil-off gas stream (taken from one or more LNG storagetanks), the cleaned natural gas stream, an intermediate partiallycleaned natural gas streams in between respective gas treatment unitsand side streams obtained from a fractionation unit provided to receiveand fractionate the natural gas liquids obtained from the NGL-extractionunit (e.g. side streams from one or more methane enriched streams and/orone or more ethane enriched streams).

Because for the additional liquefaction train, which doesn't compriseNGL-extraction, there are no pressure limitations to take into accountassociated with the NGL-extraction. The additional feed pressure maytherefore be selected higher than the feed pressure to contribute toefficient cooling and liquefaction. The additional feed pressure mayeven be at least 20 bar above the feed pressure. The additional feedpressure may be above 50 bara, or even may be above 60 bara (bara=barabsolute).

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings depict one or more implementations in according with thepresent teachings, by way of example only, not by way of limitation. Inthe FIGURES, like reference numerals refer to the same or similarelements. Furthermore, a single reference number will be used toidentify a conduit or line as well as the stream conveyed by that line.

FIG. 1 is a schematic illustration of an embodiment.

DETAILED DESCRIPTION OF THE INVENTION

The following examples of certain aspects of some embodiments are givento facilitate a better understanding of the present invention. In no wayshould these examples be read to limit, or define, the scope of theinvention.

There is provided a liquid natural gas plant comprising a plurality ofliquefaction trains, of which at least one train, referred to as anadditional liquefaction train, liquefies gas streams received from theother trains (referred to as treating and liquefaction trains). Theadditional liquefaction train is preferably added to an existing plantas retrofit.

In existing plant designs, i.e. plants not comprising an additionalliquefaction train as described here, typically fuel is obtained fromgas streams obtained from the treatment and liquefaction trains, such asportions of the end flash gas and the overhead of the scrub column usedfor NGL-extraction, which are relatively lean and clean.

Now provided is a liquid natural gas plant in which fuel is mainlyobtained from the natural gas feed stream upstream of the cooling andgas treatment units. The relatively lean and clean gas streams mentionedabove are now fed to the additional liquefaction train as additionalfeed stream.

It is recognized that the treatment required for fuel gas, i.e. for fuelgas fed to gas turbines, boilers, LNG plant furnaces) are less stringentthan the requirements for LNG. For example, for fuel gas, CO₂ removal isless stringent, heavy hydrocarbon removal is less stringent, H₂S removalis less stringent, water removal is less stringent and mercury removalis less stringent. The treatment requirements for making thecontaminated natural gas feed stream suitable for fuel, may comprisesome sort of hydrate formation control (i.e. pre-heating, dew-pointing),pressure control and possibly superheating, but over-all requires lesshardware than gas treatment to meet LNG specs.

It is therefore recognized that the relatively clean and lean gasstreams can more efficiently be liquefied to produce additional LNG,than used as fuel stream.

The additional liquefaction train can advantageously be added toexisting liquid natural gas plants comprising two or more treatment andliquefaction trains, in particular in situations wherein there isovercapacity available upstream in the NGL extraction unit and upstreamthereof.

According to WO201576975 the temperature of the main cryogenic heatexchanger is increased to ensure sufficient production of end flash gasand boil off gas to feed the small scale LNG plant. This approach isdisadvantageous, as it depends on the additional capacity available inthe main cryogenic heat exchanger. Also, changing the temperature couldtake the operating parameters outside the original design window of themain cryogenic heat exchanger, thereby resulting in a less efficientoperation. According to the current embodiments, there is no need tochange the temperature of the main cryogenic heat exchanger.

The embodiments provided here allow to operate the LNG plant includingthe additional liquefaction train, without such a need of increase ofthe temperature.

Instead of increasing the temperature of the main cryogenic heatexchanger, or more generally said: of the cold end of the train,different measures are suggested to ensure a sufficiently largeadditional feed stream to benefit from the economy of scale. One ofthese measures is to take fuel gas from another location in the plant,i.e. a position upstream of the second cooling unit (see detaileddescription below, also known as the main cryogenic heat exchanger),thereby allowing to use more clean and lean gas from the treatment andliquefaction trains to provide to the additional liquefaction train.

With reference to FIG. 1, there is provided a liquid natural gas plant(1) for producing liquefied natural gas from a contaminated natural gasfeed stream (10). The contaminated natural gas feed stream 10 mayoriginate from a pre-treatment unit 2, which is arranged to receive oneor more natural gas streams 30 from a source or well and discharge acontaminated natural gas feed stream 10 having a well-defined constantpressure, flow rate and composition. Therefore, the pre-treatment unit 2may be equipped with a slug catcher, pressure control devices,stabilizers and metering equipment. The slug catcher and the stabilizerare provided to remove heaver liquids (condensates).

The liquid natural gas plant comprises two or more parallel treatmentand liquefaction trains A, B. According to an embodiment, the liquidnatural gas plant 1 comprises three or more parallel treatment andliquefaction trains, for instance four or six parallel treatment andliquefaction trains. The term parallel is used to indicate that thetrains are arranged to process portions of the contaminated natural gasfeed stream in parallel. There may however be integration between theparallel treatment and liquefaction trains A, B, for instance by havingshared refrigerant loops, shared utility functionality, sharedrefrigerant make-up facilities.

The respective treatment and liquefaction trains A, B comprise an inlet11 for receiving a portion of the contaminated natural gas feed stream10′, 10″. The inlet 11 may be in fluid communication with thepre-treatment unit 2 described above.

The respective treatment and liquefaction trains A, B may furthercomprise a gas treatment stage 12. The gas treatment stage is arrangedto receive the respective portion 10′, 10″ of the contaminated naturalgas feed stream 10 and remove certain contaminants therefrom. The gastreatment stage 12 may comprise one or more of the following gastreatment units:

-   -   acid gas removal unit (AGRU) to remove acid components, CO₂        and/or H₂S, the acid gas removal unit comprising equipment for        separation purposes, such as an absorption column, a regenerator        column including reboilers, condensers and other heat        exchangers, wherein the absorption column and regenerator column        comprise internals, e.g. trays or packing (structured/random),    -   dehydration unit to remove H₂O, and    -   mercury removal unit to remove mercury, and

The acid gas removal unit (AGRU) may also remove aromatic components(co-absorption), to help achieving benzene/aromatics specifications forliquefaction.

The gas treatment stages 12 comprise an outlet for discharging a cleanednatural gas stream 13. The gas treatment stages 12 may also comprise oneor more outlets for respective contaminant streams 36. The respectivetreatment and liquefaction trains A, B comprise a cooling stage 14 influid connection with the outlet of the gas treatment stage 12 toreceive the cleaned natural gas stream 13.

The cooling stage 14 is equipped to cool and optionally liquefy at leastpart of the cleaned natural gas stream 13 received. The cooling stage 14may comprise any suitable cooling process, such as Single MixedRefrigerant (SMR) process, Double Mixed Refrigerant (DMR) process,Cascade process, C3MR process, Liquefin™ process as well as expansionbased cooling processes. It will be understood that any suitable coolingprocess may be applied. The parallel treatment and liquefaction train A,B do not necessarily comprise the same cooling process.

By way of example, FIG. 1 schematically shows a cooling processcomprising a first cooling unit 15, e.g. using a first refrigerant, anda second cooling unit 17, using a second refrigerant. The firstrefrigerant may be a first mixed refrigerant and the second refrigerantmay be a second mixed refrigerant (DMR process). Alternatively, thefirst refrigerant may be a single component refrigerant (typicallypropane) and the second refrigerant may be a second mixed refrigerant(SMR process).

Depending on the cooling process and the operating parameters, thecooling stage 14 cools and liquefies at least part of the cleanednatural gas stream 13, or only cools at least part of the cleanednatural gas stream 13, while the phase transition to liquid takes placedownstream thereof, e.g. in an end flash unit (described below).

The first cooling unit 15 is arranged to generate a pre-cooled cleanednatural gas stream 151. The second cooling unit 17 is arranged togenerate a further cooled stream 171 (being at an operatingtemperature). The further cooled stream may be substantially liquid(i.e. more than 99 mol % liquid) at the outlet pressure of the secondcooling unit 17 (main cryogenic heat exchanger (MCHE)). In treatment andliquefaction train(s) A, including an end-flash unit 18 (as will bedescribed in more detail below), the conditions of the further cooledstream 171′ are selected such to produce a liquefied natural gas stream184 and end flash stream 182 by means of reducing pressure andseparation of liquid and vapor phases (described in more detail below).In treatment and liquefaction trains(s) B (a train not comprising anend-flash unit), the conditions of the further cooled stream 171″ areselected such to produce a liquefied natural gas stream 186. Theliquefied natural gas stream 186 is substantially liquid. Herein, avapor phase may be separated from the liquefied natural gas stream 186in the LNG storage tank 100. Such vapor is commonly referred to asboil-off gas (BOG). This process may be referred to as flash-in-tank.Further cooled stream 171″ may be a sub-cooled liquid before pressurelet down and may typically contain, for instance, about 1-3 mol % vapourafter pressure let down. This vapour will be separated, for instance, inthe LNG storage tank 100.

It will be understood that many variations exist, which variationstypically are the amount of vapor generated and the location where vaporis generated (in LNG storage tank 100 or in end flash unit 18).

Although schematically shown as separate blocks, it will be understoodthat the first and second cooling units 15, 17 may be integrated. Forinstance, the second (mixed) refrigerant may be passed through the firstcooling unit 15 to be pre-cooled by the first (mixed) refrigerant.

According to the embodiments, the cooling stage 14 comprises aNGL-extraction unit 16 (also known as a NGL removal unit) for extractingnatural gas liquids 161 from the cleaned natural gas stream 13. NaturalGas Liquids (NGLs) are hydrocarbon molecules having two or more carbonatoms (C₂ ⁺-molecules), such as ethane, propane etc.

According to the embodiment schematically depicted in FIG. 1, theNGL-extraction unit 16 is positioned in between the first and secondcooling units 15, 17. The NGL extraction unit 16 is therefore arrangedto receive the pre-cooled cleaned natural gas stream 151 from the firstcooling unit 15. However, other line-ups may be conceivable, forinstance depending on the cooling process and gas composition.

The NGL-extraction unit 16 may be a scrub column or any other suitableseparator, including a flash vessel. The appropriate NGL-extraction unit16 depends on the liquid content of the feed gas. For instance, pipelinegas typically contains little NGLs, while associated gas typicallycontains high amounts of NGLs.

The NGL-extraction unit 16 discharges a natural gas liquid stream 161,which may also be referred to as a C₂ ⁺-enriched stream 161. The term C₂⁺-enriched is used to indicate that the stream is enriched in C₂ ⁺molecules compared to the stream received by the NGL extraction unit 16,in this embodiment stream pre-cooled cleaned natural gas stream 151.

The natural gas liquid stream 161 may be passed on to a fractionationunit, comprising a fractionation column or series of fractionationcolumns (de-methanizer, de-ethanizer, de-propanizer, etc.), to furtherseparate the components of the natural gas liquid stream 161. Thefractionation unit, in use, may generate a methane enriched stream andan ethane enriched stream. The methane enriched stream is enriched inmethane compared to the natural gas liquid stream 161. The ethaneenriched stream is enriched in ethane compared to the natural gas liquidstream 161.

Some components may be stored separately for separate sale orrefrigerant make-up; other components may be fed back to the coolingstage 14, e.g. methane that came with the natural gas liquid stream 161.

According to an embodiment, the additional feed stream may comprise afurther stream comprising at least a portion of the one or more methaneenriched streams generated by the respective fractionation units of therespective treatment and liquefaction trains (A, B).

According to an embodiment, the additional feed stream may comprise afurther stream comprising at least a portion of the one or more ethaneenriched streams generated by the respective fractionation units of therespective treatment and liquefaction trains (A, B).

Advantageously, the methane enriched streams and the ethane enrichedstreams are at a substantial pressure, typically in the range of 20-30bara, e.g. 25 bara, so need relatively little compression for being fedto the additional liquefaction train C.

The NGL-extraction unit 16 further discharges a light natural gas stream162, in fact being the stream received by the NGL-extraction unit 16without the natural gas liquid stream 161, which light natural gasstream 162 is at least partially to be further cooled by the secondcooling unit 17 and to be at least partially liquefied to generateliquefied natural gas 181. The light natural gas stream 162 may also bereferred to as C₁-enriched stream 162.

The term C₁-enriched is used to indicate that the stream is enriched inC₁ molecules (methane) compared to the stream received by the NGLextraction unit 16, in this embodiment stream pre-cooled cleaned naturalgas stream 151.

The respective treatment and liquefaction trains A, B comprise an outlet181 for discharging liquefied natural gas. According to the embodimentschematically depicted in FIG. 1, the liquefied natural gas streams 181discharged by the outlets 181 are collected in a LNG storage tank 100.However, it will be understood that more than one LNG storage tank 100may be present, and not all trains are necessarily connected to all LNGstorage tanks 100.

The liquid natural gas plant 1 comprises an additional liquefactiontrain C.

The additional liquefaction train C can be added as retrofit to anexisting LNG plant 1, or can be part of the original design of a LNGplant. Retrofitting may in particular be advantageous in situations inwhich there is overcapacity in the warm end, i.e. in the NGL-extractionunit 16 and upstream thereof, which may for instance be the case whenthere is a change in the composition of the feed gas, e.g. less CO₂content, or as a result of (partial) replacement of the equipment forseparation purposes of the acid gas removal unit (as described above)and/or retrofitting/expanding other equipment of the acid gas removalunit, such as heat exchangers, allowing a higher throughput through thegas treatment stage 12. It will be understood that replacement of theequipment for separation purposes of the acid gas removal unit, inparticular a replacement of internals of the absorption column, and/orreplacement/expansion of smaller equipment is a relativelycost-efficient way to increase the throughput of the gas treatment stage12, in case the acid gas removal unit is the constraining part of thegas treatment stage 12.

Also, retrofitting may be advantageous in case the existing LNG plantwas originally overdesigned.

It is noted that the additional liquefaction train C preferably does notcomprise gas treatment, i.e. does not comprise an acid gas removal unit,dehydration unit, mercury removal unit and co-absorption unit, and theadditional liquefaction train further doesn't comprise NGL-extraction.

According to an embodiment, the additional liquefaction train Ccomprises less gas treatment units than the treatment and liquefactiontrains A, B. For instance, in case the treatment and liquefaction trainsA, B comprise four gas treatment units, e.g. an acid gas removal unit(AGRU), a dehydration unit, a mercury removal unit, and a co-absorptionunit, while the additional liquefaction train comprises no more than asubset thereof (three or less gas treatment units).

The additional liquefaction train comprises an additional cooling stage214 arranged to receive and liquefy an additional feed stream 210thereby generating additional liquefied natural gas. The additionalcooling stage C may again use any suitable cooling process, such as theexamples provided above, and may be similar or different to the coolingprocesses comprised by the treatment and liquefaction trains A, B.

According to the embodiment depicted in FIG. 1, the additionalliquefaction train C comprises a similar cooling stage as the treatmentand liquefaction trains A, B described above, i.e. comprises a firstcooling unit 215 is arranged to generate a pre-cooled natural gas stream2151 and a second cooling unit 217 is arranged to generate a furthercooled stream 2171. The second cooling unit 217 is arranged to receivethe pre-cooled cleaned natural gas stream 2151 from the first coolingunit 215 directly.

The additional liquefaction train C optionally comprises an end-flashunit 218, which is arranged to receive the further cooled stream 2171and discharge a flash stream 282 and a liquid natural gas stream 284 viaoutlet 281.

The additional liquefaction train C receives an additional feed stream210 which comprises at least two side streams 163 taken from therespective light natural gas streams 162 discharged by theNGL-extraction units 16 of the one or more parallel treatment andliquefaction trains (A, B). The at least two side streams 163 aresubstantially gaseous. Depending on the pressure of the at least twoside streams 163, the side streams 163 may be passed through acollecting and compression unit 202, described in more detail below. Thesecond cooling unit 217 can directly receive the pre-cooled cleanednatural gas stream 2151 from the first cooling unit 215, because NGL 161has already been removed from the additional feed stream 210 by the NGLextraction units 16 of the respective treatment and liquefaction trainsA, B.

The additional liquefaction train C may be a stand-alone train, i.e.being separate from the treatment and liquefaction trains A, B. However,the additional liquefaction train C may also be integrated with the oneor more treatment and liquefaction trains A, B, for instance, by sharingrefrigerant make-up facilities, utilities, etc.

According to an embodiment, one or more of the parallel treatment andliquefaction trains (A) comprise an end flash unit 18 arranged toreceive and flash at least part of the further cooled stream 171 togenerate an end flash stream 182 and a liquefied natural gas stream 184.The end flash stream 182 is substantially gaseous. The liquefied naturalgas stream 184 is substantially liquid. Herein, the additional feedstream 210 may further comprise at least a portion of the one or moreflash streams 182 generated by the respective end flash units 18 of theone or more of the parallel treatment and liquefaction trains (A).

The end-flash unit 18 may be positioned downstream of the cooling stage14 and arranged to receive (part of) the further cooled stream 171.

FIG. 1 shows one train with end flash unit 18 and one train without endflash unit 18, but it will be understood that any number of the paralleltreatment and liquefaction trains present may comprise an end flash unit18, including none and all.

In addition to only using side streams 163 taken from the respectivelight natural gas streams 162 from the NGL extraction unit 16, end-flashgas 182 may be used in addition. In use, any suitable portion of the endflash stream 182 may be used, ranging from 0% to 100%. The portion ofthe end flash stream 182 not fed to the additional liquefaction train C,may be used for fuel or may be flared.

According to an embodiment, the entire flash streams 182 of one or moretreatment and liquefaction trains A comprising an end flash unit 18 arecomprised by the additional feed stream. According to an embodiment, theentire flash streams 182 of all the treatment and liquefaction trains Acomprising an end flash unit 18 are comprised by the additional feedstream.

As the flash streams 182 are already relatively clean and lean, theadditional liquefaction train C doesn't require (all of the) a gastreatment stage or NGL-extraction unit.

According to an embodiment, the flash streams 182 are first passedthrough the respective cooling stages of the treatment and liquefactiontrains A from which they are obtained for cold-recovery purposes beforebeing (partially) passed on to the additional liquefaction train C.

The different streams to be comprised in the additional feed stream 210may not all be at the same pressure and may not (all) be at a suitablepressure. This is in particular the case when the additional feed stream210 also comprises (a portion of) flash streams 182, as flash streamsare typically at a relatively low pressure, such as close to ambient.

According to an embodiment the liquid natural gas plant 1 comprises acollecting and compression unit 202, comprising a plurality of inlets toreceive the respective streams to be comprised by the additional feedstream 210. The collecting and compression unit 202 is arranged topressurize and combine the different streams to form and discharge theadditional feed stream.

The collecting and compression unit 202 may comprise a single ormultistage compressor 203, optionally with inter and/or after-coolers(not shown), to compress the streams to be comprised by the additionalfeed stream to a predetermined additional feed pressure. The compressor203 may have one or more inlets allowing inflow of streams withdifferent pressures.

In a further embodiment, the driver of the compressor 203 ismechanically or electrically connected to the driver of one or morerefrigerant compressors in train C. The additional liquefaction train Cmay comprise one or more refrigerant compressors arranged to compressrefrigerant, being part of the refrigeration loop, as will be understoodby a skilled person. Combination of compressors to a driver (lessdrivers than compressors) enables a better matching of driver(s) powerto compressor(s) power, especially if the drivers are gas turbines,thereby benefitting of the economy of scale of less but larger drivers,for the same capacity of additional liquefaction train C.

In a further embodiment, the additional feed pressure (stream 210) isselected such that the compressor power for compressor 203 and therefrigerant compressor power for additional cooling stage 214 areselected to further match driver and compressor power.

The additional feed pressure may be selected substantially higher thanthe feed pressure of the contaminated natural gas feed stream 10 for thetreatment and liquefaction trains A, B. Since preferably noNGL-extraction is required in the additional train C, there are nopressure limitations/considerations to take into account associated withthe NGL-extraction. NGL-extraction typically takes place at apredetermined pressure, typically in the range of 30-60 bara, e.g. 50bara, depending on the optimal conditions for performing NGL extractionfor the particular composition of the stream. NGL-extraction ispreferably done at a relatively low pressure, while liquefaction cantypically be done more efficiently at a relatively higher pressure.These two effects need to be balanced. The absence of NGL-extraction inthe additional liquefaction train C eliminates this balancing and allowsfor a more optimal pressure for liquefaction.

A relatively high pressure in the NGL-extraction units of the treatmentand liquefaction trains A, B minimizes the need for (re-)compression ofthe two or more side streams (163) taken from the respective lightnatural gas streams (162) to be comprised in the additional feed stream.

According to an embodiment, the additional feed pressure of theadditional feed stream 210 may be more than 10 bar higher than the feedpressure of the contaminated natural gas feed stream 10, more preferablyeven more than 20 bar higher. The higher additional feed pressurecontributes to more efficient cooling and liquefaction of the additionalfeed stream.

The one or more compressors may be suitable to compress the streams tobe comprised by the additional feed stream to a pressure that is morethan 10 bar of even more than 20 bar above a feed pressure at which thecontaminated natural gas feed stream (10, 10′, 10″) is received by theparallel treatment and liquefaction trains (A, B).

In embodiments in which the additional feed stream 210 comprises atleast a portion of one or more flash streams 182, the additional feed210 stream may be relatively rich in nitrogen.

According to an embodiment the liquid natural gas plant comprises anitrogen removal stage (not shown), the nitrogen removal stage beingarranged to receive one or more streams to be comprised by theadditional feed stream and discharge one or more nitrogen depletedstreams.

The nitrogen removal stage (also referred to as nitrogen removal unit)may be incorporated in the additional liquefaction train C, maybeincorporated in the collecting and compression unit 202 or may beincorporated in between the end flash unit 18 and upstream of thecollecting and compression unit 202/additional liquefaction train C. Inthe latter embodiment, there is preferably a single nitrogen removalstage provided to process all the end flash streams to be comprised bythe additional feed stream 210. The nitrogen removal stage comprises anoutlet arranged to discharge the one or more nitrogen depleted streams,the outlet being in fluid communication with the collecting andcompression unit 202 or with the collecting and compression unit 202.

However, the use of an additional liquefaction train as described may inparticular be suitable in situations wherein the contaminated naturalgas feed stream 10 has a low nitrogen content, which would eliminate therequirement for a nitrogen removal stage as additional treatment step,i.e. would eliminate the requirement for a nitrogen removal stage to becomprised by the additional liquefaction train C or positioned upstreamthereof.

According to an embodiment, the natural gas feed stream 10 preferablyhas a nitrogen content of less than 1.0 mol % or less than 0.5 mol %.

More specifically, the nitrogen content of the portion of thecontaminated natural gas feed stream 10′ provided to treatment andliquefaction train A comprising an end flash unit 18 is preferably lessthan 0.5 mol %, while the nitrogen content of the portion of thecontaminated natural gas feed stream 10″ provided to treatment andliquefaction train B, not comprising an end flash unit 18, is preferablyless than 1.0 mol %.

FIG. 1 further shows a fuel unit 300. The fuel unit 300 is depictedschematically and comprises a fuel inlet 301 to receive a fuel stream,comprising a side stream 32 of the contaminated natural gas feed stream10. The fuel unit 300 is arranged to burn the fuel stream to generatepower (electricity) to provide power or energy (heat) to LNG plant 1,including in particular gas turbine drivers for refrigerant compressors,gas turbine generators for electrical power generation, fuel for theheat transfer furnaces/steam boilers, flare pilots and to supply fuelfor heat demand, in particular gas treatment stage 12 may require heat.In FIG. 1 the parts of the liquid natural gas plant requiring power fromthe fuel unit 300 are schematically indicated by power consumers 302.

The fuel stream comprises at least a portion 32 of the contaminatednatural gas feed stream 10. Preferably, at least 50% of the fuel streamis formed by the fuel side-stream 32 of the contaminated natural gasfeed stream 10, a portion 34 of the end flash stream 182, and/or aportion of the cleaned natural gas stream 13.

According to an embodiment, there is provided a method of retrofitting aliquid natural gas plant comprising at least two or more firstliquefaction trains A, B arranged in parallel with an additionalliquefaction train C. After completing the retrofit, the liquid naturalgas plant 1 can be operated with a flow rate for the contaminatednatural gas feed stream 10 as outputted by the pretreatment unit 2,which can be increased with respect to a flow rate for the contaminatednatural gas feed stream 10 prior to the retrofit (i.e. withoutadditional train C).

Preferably the fuel side stream is taken from the contaminated naturalgas feed stream 10. However, in situations where the contaminatednatural gas feed comprises relatively high amounts of H₂S, the fuelside-stream is preferably taken from the cleaned natural gas stream 13.

According to an embodiment, the liquid natural gas plant comprises atleast four or more parallel treatment and liquefaction trains (A, B).

The treatment and liquefaction trains preferably each have a capacity ofat least 2 mmtpa, preferably at least 3 mmtpa (mmtpa million metrictonnes of LNG per year). This way the additional liquefaction train (C)may have a capacity of at least 2 mmtpa to benefit from economy ofscale.

Also, in case the additional liquefaction train is added to an existingliquid natural gas plant, having at least four or more, e.g. six,parallel treatment and liquefaction trains with the above mentionedcapacity, a sufficiently large additional feed stream can be generatedwithout the need to change the operating parameters of the existingparallel treatment and liquefaction trains.

According to an embodiment there is provided a method of retrofitting anexisting liquid natural gas plant to increase the liquefied natural gasproduction capacity thereof. The resulting liquid natural gas plant maybe referred to as a retrofitted liquid natural gas plant.

The existing liquid natural gas plant (1) may comprise two or moreparallel treatment and liquefaction trains (A, B) as described above,which are arranged to

-   -   receive a portion of a contaminated natural gas feed stream        (10′, 10″),    -   remove contaminants from the respective portion of the        contaminated natural gas feed stream (10′, 10″) thereby        generating a cleaned natural gas stream (13),    -   cool at least part of the cleaned natural gas stream (13) and        extract natural gas liquids (161) from the cleaned natural gas        stream (13), thereby generating a light natural gas stream (162)        to be at least partially further cooled by the cooling stage        (14).

The method of retrofitting comprises

-   -   providing an additional liquefaction train (C), the additional        liquefaction train comprising an additional cooling stage        arranged to receive and liquefy an additional feed stream (210)        thereby generating additional liquefied natural gas. The        additional liquefaction train may be as described above, i.e.        may not comprise NGL-extraction and/or gas treatment.

The method of retrofitting comprises

-   -   fluidly connecting the additional liquefaction train (C) to two        or more of the light natural gas streams (162) of two or more of        the treatment and liquefaction trains (A, B) to obtain side        streams (163) of the two or more light natural gas streams to be        comprised in the additional feed stream (210).

In case the existing liquid natural gas plant comprises one or moreparallel treatment and liquefaction trains (A) comprising an end flashunit (18) as described above, the method of retrofitting may comprise

-   -   fluidly connecting the additional liquefaction train (C) to one        or more of the end flash streams (182) to receive at least a        portion thereof to be comprised in the additional feed stream        (210).

The method of retrofitting may comprise

-   -   providing a collecting and compression unit (202) comprising a        plurality of inlets to receive the respective streams to be        comprised by the additional feed stream from the two or more        parallel treatment and liquefaction trains (A, B), the        collecting and compression unit comprising one or more        compressors to compress the streams to be comprised by the        additional feed stream to a predetermined additional feed        pressure and combine the streams to be comprised by the        additional feed stream to form the additional feed stream, the        collecting and compression unit (202) further comprising an        outlet to discharge the additional feed stream (210),    -   fluidly connecting the respective inlets of the collecting and        compression unit (202) with the two or more parallel treatment        and liquefaction trains (A, B) and fluidly connecting the outlet        of the collecting and compression unit (202) with the additional        liquefaction train (C).

The respective inlets of the collecting and compression unit are fluidlyconnected with those streams of the parallel treatment and liquefactiontrains from which gas is taken to be comprised in the additional feedstream 210.

According to an embodiment, the existing liquid natural gas plantcomprises a fuel unit (300), the fuel unit (300) being arranged toreceive and burn a fuel stream, thereby generating power and/or heat toprovide the liquid natural gas plant (1) with energy and/or heat,wherein the method of retrofitting comprises

-   -   fluidly connecting the fuel unit (300) to receive a side-stream        of the contaminated natural gas feed stream (10) or the cleaned        natural gas stream (13).

The existing liquid natural gas plant may comprise a fluid fuelconnection between the fuel unit and the respective parallel treatmentand liquefaction trains, e.g. between the fuel unit and end flashstreams (182), to provide the fuel unit with fuel. The method ofretrofitting may comprise disconnecting this fuel connection. The methodof retrofitting may also comprise leaving the existing fuel connectionin place, but in use, the flow rate through the existing fuel connectionwill be significantly reduced compared to prior to the retrofit,typically reduced with more than 50%.

As described above, the treatment and liquefaction trains may comprise afirst cooling unit 15 and a second cooling unit 17, the second coolingunit generating a further cooled stream 171 being at an operatingtemperature, wherein the operating temperature in the treatment andliquefaction trains A, B is substantially equal prior and afterretrofitting. The term substantial equal is used here to indicate thatthe operating temperatures differ less than 4° C., preferably less than2° C.

Once a retrofitted liquid natural gas plant has been provided, theretrofitted liquid natural gas plant may be operated, wherein the methodof operating comprises

-   -   receiving the respective portions of the contaminated natural        gas feed streams (10′, 10″) at a feed pressure and    -   pressurizing the additional feed stream to an additional feed        pressure, being at least 10 bar above the feed pressure,    -   feeding the additional feed stream to the additional        liquefaction train (C).

According to an embodiment, the additional feed pressure of theadditional feed stream 210 may be more than 10 bar higher than the feedpressure of the contaminated natural gas feed stream 10, more preferablyeven more than 20 bar higher. The higher additional feed pressurecontributes to more efficient cooling and liquefaction of the additionalfeed stream.

The present disclosure is not limited to the embodiments as describedabove and the appended claims. Many modifications are conceivable andfeatures of respective embodiments may be combined.

ADDITIONAL EMBODIMENTS

According to a further embodiment, there is provided a liquid naturalgas plant (1) for producing liquefied natural gas from a contaminatednatural gas feed stream (10), the liquid natural gas plant (1)comprising one or more parallel treatment and liquefaction trains (A,B), wherein the respective treatment and liquefaction trains (A, B)comprise:

-   -   an inlet (11) for receiving a portion of the contaminated        natural gas feed stream (10′, 10″),    -   a gas treatment stage (12) for removing contaminants from the        respective portion of the contaminated natural gas feed stream        (10′, 10″) thereby generating a cleaned natural gas stream (13),    -   a cooling stage (14) arranged to receive the cleaned natural gas        stream (13) from the gas treatment stage (12) for cooling at        least part of the cleaned natural gas stream (13), wherein the        cooling stage (14) comprises a NGL-extraction unit (16) for        extracting natural gas liquids (161), thereby generating a light        natural gas stream (162) to be at least partially further cooled        by the cooling stage (14) to be at least partially liquefied and    -   an outlet (181) for discharging liquefied natural gas,

wherein the liquid natural gas plant (1) comprises an additionalliquefaction train (C), the additional liquefaction train comprising

-   -   an inlet (211) for receiving an additional feed stream (210),    -   an additional cooling stage (214) arranged to receive the        additional feed stream for cooling the additional feed stream        (210) thereby generating additional liquefied natural gas, and    -   an outlet (281) for discharging the additional liquefied natural        gas (284),

wherein the additional feed stream (210) comprises one or more sidestreams (163) taken from the respective light natural gas streams (162)of the one or more parallel treatment and liquefaction trains (A, B).

According to a further embodiment there is provided a method ofretrofitting an existing liquid natural gas plant to increase theliquefied natural gas production capacity thereof, wherein the existingliquid natural gas plant (1) comprises one or more parallel treatmentand liquefaction trains (A, B) for producing liquefied natural gas froma contaminated natural gas feed stream (10), wherein the one or moreparallel treatment and liquefaction trains (A, B) are arranged to

-   -   receive a portion of a contaminated natural gas feed stream        (10′, 10″),    -   remove contaminants from the respective portion of the        contaminated natural gas feed stream (10′, 10″) thereby        generating a cleaned natural gas stream (13),    -   cool at least part of the cleaned natural gas stream (13) and        extract natural gas liquids (161), thereby generating a light        natural gas stream (162) to be at least partially further cooled        by the cooling stage (14),

wherein the method of retrofitting comprises

-   -   providing an additional liquefaction train (C), the additional        liquefaction train comprising an additional cooling stage        arranged to receive and liquefy an additional feed stream (210)        to generate additional liquefied natural gas,    -   fluidly connecting the additional liquefaction train (C) to one        or more of the light natural gas streams (162) of one or more of        the treatment and liquefaction trains (A, B) to obtain side        streams (163) of the one or more light natural gas streams to be        comprised in the additional feed stream (210), thereby creating        a retrofitted liquid natural gas plant.

According to a further embodiment there is provided a method ofoperating a retrofitted liquid natural gas plant (1) according to theabove or being provided according to method or retrofitting providedabove, wherein the method comprises

-   -   operating the one or more parallel treatment and liquefaction        trains (A, B) whereby operating the one or more parallel        treatment and liquefaction trains (A, B) comprises receiving        respective portions of the contaminated natural gas feed streams        (10′, 10″) by the one or more parallel treatment and        liquefaction trains (A, B) at a feed pressure and    -   operating the additional liquefaction train (C), whereby        operating the additional liquefaction train (C) comprises        providing an additional feed stream comprising one or more light        natural gas streams (163) taken from the one or more parallel        treatment and liquefaction trains (A, B), wherein the additional        feed stream is provided at an additional feed pressure, being at        least 10 bar above the feed pressure.

It is recognized that an additional liquefaction train may also be addedto a single treatment and liquefaction train. The additional feed streammay comprise any combination of the above disclosed streams taken fromthe (single) treatment and liquefaction trains, such as end flash.

1. A liquid natural gas plant for producing liquefied natural gas from acontaminated natural gas feed stream, the liquid natural gas plantcomprising two or more parallel treatment and liquefaction trainsarranged in process portions of the contaminated natural gas feed streamin parallel, the treatment and liquefaction trains each comprising: aninlet for receiving a portion of the contaminated natural gas feedstream, a gas treatment stage for removing contaminants from therespective portion of the contaminated natural gas feed stream therebygenerating a cleaned natural gas stream, a cooling stage arranged toreceive the cleaned natural gas stream from the gas treatment stage forcooling at least part of the cleaned natural gas stream, wherein thecooling stage comprises a NGL-extraction unit for extracting natural gasliquids, thereby generating a light natural gas stream to be at leastpartially further cooled by the cooling stage to be at least partiallyliquefied; and an outlet for discharging liquefied natural gas, whereinthe liquid natural gas plant comprises at least one additionalliquefaction train, the additional liquefaction train comprising: aninlet for receiving an additional feed stream, an additional coolingstage arranged to receive the additional feed stream for cooling theadditional feed stream thereby generating additional liquefied naturalgas, and an outlet for discharging the additional liquefied natural gas,wherein the additional feed stream comprises at least two or more sidestreams taken from the respective light natural gas streams, of the twoor more parallel treatment and liquefaction trains.
 2. The liquidnatural gas plant according to claim 1, wherein one or more of theparallel treatment and liquefaction trains comprise an end flash unitarranged to receive and flash at least part of the respective lightnatural gas streams to generate an end flash stream and liquefiednatural gas, wherein the additional feed stream further comprises atleast a portion of the one or more flash streams generated by therespective end flash units.
 3. The liquid natural gas plant according toclaim 1, wherein the liquid natural gas plant comprises a collecting andcompression unit, comprising a plurality of inlets to receive therespective streams to be comprised by the additional feed stream. Thecollecting and compression unit is arranged to pressurize and combinethe different streams to form and discharge the additional feed stream.4. The liquid natural gas plant according to claim 1, wherein the liquidnatural gas plant comprises a nitrogen removal stage, the nitrogenremoval stage being arranged to receive one or more streams to becomprised by the additional feed stream and discharge one or morenitrogen depleted streams.
 5. The liquid natural gas plant according toclaim 1, wherein the liquid natural gas plant comprises a fuel unitcomprising a fuel inlet to receive a fuel stream, the fuel streamcomprising a side stream of the contaminated natural gas feed stream. 6.The liquid natural gas plant according to claim 1, wherein the liquidnatural gas plant comprises at least four or more parallel treatment andliquefaction trains.
 7. A method of retrofitting an existing liquidnatural gas plant to increase the liquefied natural gas productioncapacity thereof, wherein the existing liquid natural gas plantcomprises two or more parallel treatment and liquefaction trains forproducing liquefied natural gas from a contaminated natural gas feedstream, wherein the two or more parallel treatment and liquefactiontrains are arranged to process portions of the contaminated natural gasfeed stream in parallel and are each arranged to: receive a portion of acontaminated natural gas feed stream, remove contaminants from therespective portion of the contaminated natural gas feed stream therebygenerating a cleaned natural gas stream, cool at least part of thecleaned natural gas stream and extract natural gas liquids, therebygenerating a light natural gas stream to be at least partially furthercooled by the cooling stage, wherein the method of retrofittingcomprises the steps of: providing an additional liquefaction train, theadditional liquefaction train comprising an additional cooling stagearranged to receive and liquefy an additional feed stream to generateadditional liquefied natural gas, fluidly connecting the additionalliquefaction train to two or more of the light natural gas streams oftwo or more of the treatment and liquefaction trains to obtain sidestreams of the two or more light natural gas streams to be comprised inthe additional feed stream, thereby creating a retrofitted liquidnatural gas plant.
 8. The method of retrofitting according to claim 7,wherein the existing liquid natural gas plant comprises one or moreparallel treatment and liquefaction trains comprising an end flash unit,the method of retrofitting comprising fluidly connecting the additionalliquefaction train (C) to one or more of the end flash streams toreceive at least a portion thereof to be comprised in the additionalfeed stream.
 9. The method of retrofitting according to claim 7,comprising providing a collecting and compression unit comprising aplurality of inlets to receive the respective streams to be comprised bythe additional feed stream from the two or more parallel treatment andliquefaction trains, the collecting and compression unit comprising oneor more compressors to compress the streams to be comprised by theadditional feed stream to a predetermined additional feed pressure andcombine the streams to be comprised by the additional feed stream toform the additional feed stream, the collecting and compression unitfurther comprising an outlet to discharge the additional feed stream,fluidly connecting the respective inlets of the collecting andcompression unit with the two or more parallel treatment andliquefaction trains and fluidly connecting the outlet of the collectingand compression unit with the additional liquefaction train.
 10. Themethod of retrofitting according to claim 7, wherein the existing liquidnatural gas plant comprises a fuel unit, the fuel unit being arranged toreceive and burn a fuel stream, thereby generating power and/or heat toprovide the liquid natural gas plant with energy and/or heat, whereinthe method of retrofitting comprises the step of: fluidly connecting thefuel unit to receive a side-stream of the contaminated natural gas feedstream or the cleaned natural gas stream.
 11. A method of operating aliquid natural gas comprising the steps of: operating the two or moreparallel treatment and liquefaction trains whereby operating the two ormore parallel treatment and liquefaction trains comprises receivingrespective portions of the contaminated natural gas feed stream by thetwo or more parallel treatment and liquefaction trains at a feedpressure and processing said portions of the contaminated natural gasfeed stream in parallel, and operating the additional liquefactiontrain, whereby operating the additional liquefaction train comprisesproviding an additional feed stream comprising at least two or morelight natural gas streams taken from the two or more parallel treatmentand liquefaction trains, wherein the additional feed stream is providedat an additional feed pressure, being at least 10 bar above the feedpressure.